The tools and resources are now available for the development of screens for genes that enhance metastasis in vivo. Such screens will identify new targets for drug development that may complement therapies currently under development or in clinical use. In addition, the information provided by such screens will aid in reducing the number of potential targets that are identified through microarray studies by indicating which gene products are likely to be driving metastasis. We propose to combine high throughput gene expression and suppression technologies with in vivo metastasis methodology to accelerate in vivo screening by a factor of up to 50. The screen will indicate the contributions of proteins to the steps of primary tumor growth, intravasation, and lung colonization. The first aim will focus on production of pools of cells expressing or suppressing selected proteins. The second aim will evaluate detection technologies for measuring construct distributions in a pool. The third aim will determine the appropriate formation of pools to be screened. The fourth and fifth aims will perform an initial screen and validate candidates identified in the screen. This R21 application will enable the development of the screen and demonstrate feasibility; providing a paradigm for evaluating gene function for the most critical feature of tumor cell malignancy - the ability to metastasize. [unreadable] [unreadable] ASSESSMENT: [unreadable] [unreadable] [unreadable]